Oxidation Resistance and Strength of TiAl Based Alloys in a Simulated

研究了γ-TiAl基合金Ti-48Al-2Cr-2Nb、Ti-48Al-2Cr-2Fe、Ti-48Al-2Cr-2W和Ti-48Al-2Cr-1W-1Ta(摩尔分数)在1173K模拟燃气中的循环氧化行为，循环时间长达25次(500h)。用X射线衍射仪、扫描电子显微镜和电子探针对氧化产物和亚表面进行了分析和表征。除了一种含铁的合金外，所有合金都通过形成薄而附着的氧化物鳞片，在至少25个循环中表现出优异的抗氧化性。尤其是含W合金的增重率仅为Ti-48Al-2Cr-2Nb合金的1/3，说明W-Ta具有与W相似的显著作用。良好的抗氧化性是由于在氧化初期在鳞片中形成了一层确定致密的Al_2O_3。鳞片下方形成稳定的贫铝层(即Z相)。除了掺杂效应外，Nb、Ta和W的影响似乎也稳定了贫铝层。然而，它们因氧化而获得的质量增量比在实验室空气中测试的要小，尽管燃烧气体被认为比空气更具攻击性。另一方面，Ti-48Al-2Cr-2Fe的氧化膜由两层组成：外层为均匀分布的铁、铬氧化物的TiO2层，内层为Al_2O_3和TiO2相的混合层。

The cyclic oxidation behavior of γ - TiAl based alloys, Ti-48Al-2Cr-2Nb, Ti-48Al-2Cr-2Fe, Ti-48Al-2Cr-2W and Ti-48Al-2Cr-1W-1Ta (mol %), was studied in a simulated combustion gas at 1173 K for up to 25 cycles (500 h). The oxidation products and subsurface areas were examined and characterized by using X-ray diffractometry, SEM and EPMA. All the alloys except Fe-containing one show excellent oxidation resistance for at least up to 25 cycles by forming thin and adherent oxide scals. In particular, the mass gains of W-containing alloys are a third of that of Ti-48Al-2Cr-2Nb, indicating significant effect of W. Ta seems to behave similarly as W. The excellent oxidation resistance is attributed to the formation of a definite and dense Al_2O_3 layer in the scale during the initial oxidation stage. A stable Al-depleted layer (so-called Z phase) is formed beneath the scale. The influence of Nb, Ta, and W seems to stabilize the Al-depleted layer in addition to the doping effect. However, their mass gains due to the oxidation are smaller than those tested in laboratory air, though the combustion gas was thought more aggressive than air. On the other hand, Ti-48Al-2Cr-2Fe oxidizes rapidly with scales consisting of two layers, an outer TiO_2 layer with heterogeneously distributed iron and chromium oxides and an inner porous layer which is a mixture of Al_2O_3 and TiO_2 grains.